COIN-OR::LEMON - Graph Library

source: lemon-0.x/src/work/marci/lp/max_flow_expression.cc @ 1104:23a54f889272

Last change on this file since 1104:23a54f889272 was 1104:23a54f889272, checked in by marci, 19 years ago

small changes, a try for max flow using expression

File size: 2.2 KB
Line 
1// -*- c++ -*-
2#include <iostream>
3#include <fstream>
4
5#include <lemon/smart_graph.h>
6#include <lemon/list_graph.h>
7#include <lemon/dimacs.h>
8#include <lemon/time_measure.h>
9#include <lp_solver_wrapper_3.h>
10
11using std::cout;
12using std::endl;
13using namespace lemon;
14
15template<typename Edge, typename EdgeIndexMap>
16class PrimalMap {
17protected:
18  LPGLPK* lp;
19  EdgeIndexMap* edge_index_map;
20public:
21  PrimalMap(LPGLPK& _lp, EdgeIndexMap& _edge_index_map) :
22    lp(&_lp), edge_index_map(&_edge_index_map) { }
23  double operator[](Edge e) const {
24    return lp->getPrimal((*edge_index_map)[e]);
25  }
26};
27
28// Use a DIMACS max flow file as stdin.
29// max_flow_expresion < dimacs_max_flow_file
30
31int main(int, char **) {
32
33  typedef ListGraph Graph;
34  typedef Graph::Node Node;
35  typedef Graph::Edge Edge;
36  typedef Graph::EdgeIt EdgeIt;
37
38  Graph g;
39 
40  Node s, t;
41  Graph::EdgeMap<int> cap(g);
42  readDimacs(std::cin, g, cap, s, t);
43  Timer ts;
44 
45  typedef LPGLPK LPSolver;
46  LPSolver lp;
47  lp.setMaximize();
48  typedef LPSolver::ColIt ColIt;
49  typedef LPSolver::RowIt RowIt;
50  typedef Graph::EdgeMap<ColIt> EdgeIndexMap;
51  EdgeIndexMap edge_index_map(g);
52  PrimalMap<Edge, EdgeIndexMap> lp_flow(lp, edge_index_map);
53
54  // capacity function
55  for (Graph::EdgeIt e(g); e!=INVALID; ++e) {
56    ColIt col_it=lp.addCol();
57    edge_index_map.set(e, col_it);
58    if (cap[e]==0)
59      lp.setColBounds(col_it, LPSolver::FIXED, 0, cap[e]);
60    else
61      lp.setColBounds(col_it, LPSolver::DOUBLE, 0, cap[e]);
62  }
63 
64  for (Graph::NodeIt n(g); n!=INVALID; ++n) {
65    LPSolver::Expression expr;
66    for (Graph::OutEdgeIt e(g, n); e!=INVALID; ++e)
67      expr+=edge_index_map[e];
68    for (Graph::InEdgeIt e(g, n); e!=INVALID; ++e)
69      expr-=edge_index_map[e];
70    // cost function
71    if (n==s) {
72      lp.setObjCoeffs(expr);     
73    }
74    // flow conservation
75    if ((n!=s) && (n!=t)) {
76      RowIt row_it=lp.addRow();
77      lp.setRowCoeffs(row_it, expr);
78      lp.setRowBounds(row_it, LPSolver::FIXED, 0.0, 0.0);
79    }
80  }
81  lp.solveSimplex();
82  //std::cout << lp.colNum() << std::endl;
83  //std::cout << lp.rowNum() << std::endl;
84  //std::cout << "flow value: "<< lp.getObjVal() << std::endl;
85  for (Graph::EdgeIt e(g); e!=INVALID; ++e)
86    flow.set(e, lp_flow[e]);
87}
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